This invention relates to a vibratory feeding apparatus wherein an operational frequency during a feeding operation is controlled so as to be adjusted to a resonant frequency.
In conventional vibratory feeding apparatus, a vibration generator is mainly composed of an electromagnet or piezoelectric element. In each type feeding apparatus, the operational frequency needs to be adjusted to the resonant frequency in order that the maximum feeding efficiency is gained In this regard, a vibratory feeding apparatus provided with an operational frequency adjusting function has been developed. Japanese Laid-open Patent Application No. 62-218308 discloses such a vibratory feeding apparatus wherein a CR sine-wave generator with a potentiometer is employed for adjusting the operational frequency. Gradually varying the operational frequency with the potentiometer, an operator observes the variation of the operational frequency either or both of visually and auditorily to thereby search out the resonant frequency.
In accordance with the conventional arrangement, however, the adjustment of the operational frequency to the resonant frequency depends upon either or both of the operator's eyesight and auditory sense. Accordingly, it is difficult even for a skillful operator to precisely adjust the operational frequency to the resonant frequency and therefore, variations in the frequency adjustment results in a decline in the feeding efficiency of the vibratory feeding apparatus.
Furthermore, an experiment confirms that an allowable operational frequency range lies between.+-.0.2 Hz of the resonant frequency. Since the resonant frequency has the negative temperature dependency, the resonant frequency is decreased by 2 Hz when the ambient temperature is increased from 0.degree. C. to 40.degree. C. The reason for this is that the thermal expansion of the vibration system of the apparatus varies the elastic coefficiency.
On the other hand, a capacitor of the CR oscillator employed for operational frequency adjustment has the positive temperature dependency and consequently, an output frequency of the CR oscillator is increased by 2 Hz when the ambient temperature is increased from 0.degree. C. to 40.degree. C.
Thus, The temperature gradient of the temperature dependency of the vibration system is inverse relative to that of the CR oscillator side. Consequently, when the ambient temperature is changed by+5.degree. C. even after the operational frequency is precisely adjusted to the resonant frequency at 20.degree. C., the difference between the operational and resonant frequencies approximates 0.5 Hz, which value exceeding the allowable range of the operational frequency. This signifies that the operational frequency needs to be adjusted even when the ambient temperature is slightly changed. In theses circumstances, when the operational frequency adjustment is performed depending upon either or both of the operator's eyesight and auditory sense as described above, the adjustment will become troublesome and variations in the adjusted operational frequency is caused, resulting in reduction of the feeding efficiency of the vibratory feeding apparatus.
Additionally, when an amount of articles or load on a feeding means varies during the feeding operation, the vibration amplitude of the feeding means is accordingly varies, thereby varying the feeding speed. As a result, an input voltage to the vibration generator needs to be regulated in accordance with variation in the load but it is extremely difficult to manually regulate the input voltage to the vibration generator.